1. Technical Field
This disclosure relates to subterranean structures, particularly vertical access passages to generally underground facilities, such as septic tanks and pump chambers, the vertical access passages sometimes being referred to as manholes. The present disclosure particularly to elements used in the construction of the walls of such subterranean structures, which are sometimes referred to as risers and covers therefore. The disclosure more particularly relates to cylindrical plastic structures made of a plurality of curved segments that are interlocking and stackable, and to a cover that can be locked to a variety of risers of various types.
2. Background Information
There have been previous attempts to construct the walls of manholes and other subterranean structures using a plurality of curved segments. In U.S. Pat. No. 4,751,799, a liner segment is formed in a vacuum forming operation from a heated plastic sheet, which is drawn against the surface of a suitably formed mold member to form certain prescribed outwardly extending projections. A plurality of such liner sections are then joined together using simple lap joints and placed within another mold assembly with an optional inner support and with the liner sections being spaced from the mold assembly. Concrete or other casting material is the poured into the space between the liner sections and the mold assembly with the outwardly extending projections of the liner acting to bond the liner to the casting. Other patents disclosing similar liners are U.S. Pat. Nos. 5,081,802; 5,236,298; 5,303,518; 5,383,311; 5,901,506; and 6,206,609. In all these disclosures, the liner forms a corrosion barrier for the structure, but does not have sufficient strength to constitute the only structural component of the riser.
Other liner segments can also be found, for example, in Hume U.S. Pat. No. 5,608,998, which use the liner segments to rehabilitate an existing, leaking manhole structure. The liner segments are rigid or semi-rigid plastic, and preferably corrugated, panels joined together laterally with an adhesive in a simple lap joint. A plurality of the liner segments are assembled within an existing manhole with a lower end of each ring including a channel or lip that captures the upper end of the next lower ring. Each liner segment of Hume is disclosed to include an integral L-shaped channel which is adapted to receive the opposite end of an identical panel that has no special end structure thereby permitting the panel assembly to be cut to fit a specific manhole perimeter without special forming tools. Once the liner is in place, a bonding layer of polymer foam or other material is injected between the pre-existing manhole structure and the newly formed liner. While the liner has sufficient strength to be self supporting, there is a continuing reliance on the physical strength of the pre-existing leaking manhole to provide some of the structural strength for the structure of the riser as a whole. In the event of a significant structural failure of the pre-existing leaking manhole, the simple overlapping end structure of the liner may be insufficient to prevent the manhole from collapsing inward.
Another structure formed of segments joined end to end is found in U.S. Pat. No. 4,310,372, which discloses couplings and well screens formed of three identical molded pieces joined edge to edge along longitudinal edges by C-shaped clamps slipped onto or snapped over outwardly protruding portions of the joined structure. The edges of each of the three molded pieces include various triangular ridges and grooves forming confronting, but not interlocking, surfaces, which are intended to be solvent welded together. The solvent welds in conjunction with the additional locking means provided by the C-shaped clamps hold the assembled sections together.
One-piece molded plastic structures that are intended for subterranean placement in a variety of fluid containment systems are disclosed in U.S Pat. Nos. 5,257,652; 5,333,490; 5,361,799; 5,423,447; 5,833,392; 5,988,944; 6,059,208; and 6,189,717. All of the disclosed structures rely substantially entirely on the strength of the plastic materials forming the structures to resist the forces that might be applied by the surrounding soils. Further, it is known to stack structurally self sufficient component formations from U.S. Pat. Nos. 5,617,679 and 5,852,901. While all these structures use the inherent advantages of the various disclosed polymers and plastics to achieve certain desirable results, all these structures are bulky to transport.
Underground reinforced plastic enclosures made of a plurality curved segments that are more easily transported are disclosed in U.S. Pat. Nos. 3,974,599 and 4,089,139. In the earlier of these two disclosures, the curved segments take the form of semi-cylindrical portions having confronting longitudinal edges including outwardly projecting flanges. The flanges are coupled together with bolts and nuts to form the cylindrical members from the semi-cylindrical portions. In the later of these two disclosures, a number of the curved segments, preferably three, are coupled together to form each ring of the structure. Each of the segments includes vertical side edges that are configured to provide an engaging relationship between the laterally adjacent segments. In particular, one of the vertical side edges is disclosed to include a notch formed by the inner surface of the wall segment and an intersecting inclined wall portion. The other vertical side edge includes a projecting tongue having one surface aligned approximately with the inner surface of the remainder of the wall segment and another surface angled at about the same angle as the intersecting inclined wall portion. The projecting tongue can be seen as a wedge that is adhesively secured in the notch to join adjacent segments together to form a ring, but this amounts to no more than an improved lap joint structure having increased adhesive surface area.
Subterranean openings such as vertical manholes desirably have features to prevent entry by unauthorized personnel. One such entry prevention system consists merely of a cover that desirably is locked to the side structure defining the subterranean opening. Examples of such locking covers are to be found in U.S. Pat. Nos. 897,046; 4,015,373; 4,101,154; 4,523,407; 4,964,755; 5,628,152; 5,845,442; 5,979,117; 5,987,824; and 6,584,734. Many such locking covers require a specific orientation with respect to the side structure of the subterranean opening to permit an interlocking engagement of the locking element with specific mating structures in the side structure. Some locking structures are adapted to have an outer portion that simply protrudes under a flange or ledge, but still requires manipulation of more or less complex mechanisms to achieve the necessary outward protrusion of the outer portion.
Another such entry prevention system shown in U.S. Pat. No. 5,265,974 comprises a safety net situated below the cover of a manhole type access opening. The safety net assembly has at least two rigid rods of a length sufficient to span the access opening. Each rod is supported at both ends by a support coupled to the manhole so that at least one of the rods is movable from one side of the access opening to an opposite side. A web or net is securely attached to all the rods to travel with any movement of the rods from one side of the access opening to the opposite side. The web or net has openings sufficiently small to prevent the entry of unauthorized personnel. When unlocked, the rods can be moved between a secured position and an open position.
There remains a need for a reinforced plastic enclosure suited for subterranean use as a structurally defining portion of a manhole that is constructed from a plurality of easily transported curved segments that includes vertical side edges having specific structural features that will lock adjacent segments together without a required use of any adhesive or separate fasteners. There is an additional need for a lockable lid that will cooperatively engage a top opening of a subterranean structure defined by the assembled segments. There is a further need for a security device that will inhibit accidental entry into a subterranean structure defined by the assembled segments.